Iron Fischer-Tropsch (F-T) catalysts have generally been preferred commercially over cobalt based catalysts and are presently the only commercial F-T catalyst used.
In the conversion of synas (CO+H.sub.2 mixture) in the Fischer-Tropsch reaction cobalt catalysts have the benefit of higher activity and better selectivity to motor fuels, they suffer from their inherent production of excess methane (an undesirable product) as well as the paraffinic nature of the product. It would be an important catalyst improvement if a stable cobalt F-T catalyst was discovered which demonstrated reduced methane production, increased C5+ yield and improved olefin content, especially in the C5 range.
There is a reasonable amount of prior art dealing with Fischer-Tropsch metals combined with molecular sieve components. The most recent prior art pertinent to this invention is a patent issued to J. A. Rabo et al., U.S. Pat. No. 4,652,538, and the prior ar cited within.
An excellent review of past publications on cobalt Fischer-Tropsch catalyst was reported by R. B. Anderson, "The Fischer Tropsch Synthesis", Academic Press, Orlando Fla, 1984. In the review are lists of promoters and catalysts studied in the past, included are sightings of the use of Mn and Zr promoters. Listed below is a summary of the information presented in this article related to the use of the Mn and Zr promoters. Fischer and Koch showed Mn added to a cobalt kieselguhr catalyst was effective at shifting the product distribution toward heavier product as was also observed for the catalysts in this invention. Work by Eidus and Bulanova showed a similar effect on the addition of ZrO.sub.2 to the same type of catalyst, this was not observed upon our addition of ZrO.sub.2 to the Mn promoted Co/TC-123 catalyst system. No work to our knowledge has been reported on the use of a combined Mn and Zr promoted catalyst.
Dent, A. L. and Lin, M., Adv. Chem. Ser. 178,47 (1979) reported that the addition of Mn to a cobalt alumina catalyst increased the olefin content in the product, which is consistent with our data.
The only prior art of which the applicants are aware relating to r for improving the stability of a cobalt F-T catalyst was reported by Eidus and Bulanova U.S.S.R. 150,102, Sept. 26, 1962, Appl. Nov. 27, 1954. In this work Zr was used in place of thorium to reduce the sensitivity of the catalyst to super heating.